Exercise bike



FIG. 1 is a perspective view of an exercise bike showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines shown in the drawings represent portions of the exercise bike that form no part of the claimed design. 

CLAIM The ornamental design for an exercise bike, as shown and described. 